33.1 Vertical convection

The hydrostatic approximation necessitates the use of a parameterization of vertical overturning processes. The original parameterization used by Bryan in the 1960's was motivated largely from ideas then used for modeling convection in stars. Recent work by Marshall and collaborators (Klinger et al. 1996, Marshall et al. 1997) have largely indicated that the basic ideas of vertical adjustment are useful for purposes of large-scale ocean circulation. As disscussed below, the Cox (1984) implementation of convective adjustment had the possibility of leaving columns unstable after completing the code's adjustment loop. Various full convective schemes have come on-line, with that from Rahmstorf implemented in MOM. An alternative to the traditional form of convective adjustment is to increase the vertical diffusion coefficient to some large value (say $\ge 50 cm^{2}/sec$) in order to quickly diffuse vertically unstable water columns. Indeed, it is this form which is recommended from the study of Klinger et al. (1996). The recently implemented KPP vertical mixing scheme effectively uses the large vertical diffusion coefficient approach in the context of a local and non-local vertical mixing scheme. This scheme computes the vertical diffusivity based on a series of physical and heuristic arguments (option discussed in Section 32.2.3).